Vehicles may be configured with an inlet air temperature sensor for estimating a temperature of fresh air entering a vehicle engine. Based on the intake air temperature, air mass and/or air volume estimations may be made, which may then be used for air-to-fuel ratio control. The inlet air temperature sensor may need to be periodically diagnosed to ensure proper functionality.
One example approach for diagnosing an inlet air temperature sensor is shown by Iwai in U.S. Pat. No. 7,818,997. Therein, degradation of the inlet air temperature (IAT) sensor is determined, after an engine soak duration has elapsed, based on the magnitude of deviation between a lowest temperature estimated by the IAT sensor and an engine coolant temperature estimated by a water temperature sensor.
However, the inventors herein have identified potential issues with such an approach. As an example, in hybrid vehicle systems, the vehicle may be operated without running an internal combustion engine for extended periods of time. In particular, the engine may not be operated long enough to ensure that a sufficient amount of ambient air has passed over the IAT sensor. As a result, IAT sensor results may not be reliable. In addition, there may be conditions where the diagnostic routine cannot be completed.
In one example, some of the above issues may be at least partly addressed by a method for a hybrid vehicle comprising, during vehicle operation, when intake air temperature, sensed before an engine start but after an engine soak, disagrees with engine temperature, lowering a vehicle speed threshold at which an automatic engine shutdown is enabled from a first, higher speed to a second, lower speed. In this way, engine running may be prolonged to enable a sufficient amount of ambient air to flow over the IAT sensor.
For example, following a vehicle key-on event in a hybrid vehicle, wherein the engine has sufficiently soaked, an intake air temperature (IAT) estimated by an intake air temperature sensor may be compared to an engine coolant temperature (ECT) estimated by an engine coolant temperature sensor before the engine is started. If the estimated temperatures agree (e.g., differs by less than a threshold amount), no degradation of the IAT sensor may be determined. However, if the temperatures do not agree (e.g., differs by more than the threshold amount), IAT sensor degradation may be possible. To confirm, the temperatures may be re-evaluated after a duration of engine running that ensures that sufficient air has flown over the IAT sensor. Specifically, a vehicle speed threshold at which the engine is automatically shutdown may be lowered. As such, this prolongs a duration of hybrid vehicle operation with the engine running.
The temperatures may be re-estimated after a duration of engine running while a vehicle speed is higher than a threshold, while an air mass level being higher than a threshold, and with no extended tip-out events. As such, the selected conditions reflect operating conditions that better ensure that a sufficient amount of ambient air has passed over the IAT sensor. If the re-estimated temperatures continue to disagree, then IAT sensor degradation may be confirmed. Else, if the temperatures agree upon re-evaluation, no sensor degradation is determined and the vehicle speed threshold may be reset.
In this way, IAT sensor degradation may be more reliably confirmed in a hybrid vehicle. Specifically, by verifying that sufficient fresh air mass has passed over the sensor, the integrity of the diagnostic routine is improved. By delaying automatic engine shutdowns until lower vehicle speeds, in response to an initial temperature disagreement, the diagnostic routine may be rapidly completed with reduced impact on engine-on times. By reliably and rapidly diagnosing an IAT sensor, vehicle performance is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.